1. Field of the Invention
The present invention relates to a back light module and a liquid crystal display comprising the same. More particularly, the present invention relates to a back light module with special supports for both the diffusion plate and lamp to prevent their deformation and a liquid crystal display comprising the same.
2. Description of the Related Art
To match the life style of modern people, video or imaging equipment is becoming lighter and slimmer. Although the conventional cathode ray tube (CRT) display has many advantages, the design of the electron gun renders it heavy and bulky. Moreover, there is always some risk of hurting viewer's eyes due to certain radiation emitted by the CRT. With big leaps in the techniques in manufacturing semiconductor devices and electro-optics devices, flat panel displays such as liquid crystal displays (LCD), organic light-emitting displays (OLED) and plasma display panel (PDP) have gradually become mainstream display products.
A liquid crystal display can be roughly classified into three types, namely, reflection LCD, transmissive LCD and transflective LCD. Using a transmission or a transflective LCD as an example, the LCD mainly comprises a liquid crystal panel and a back light module. The liquid crystal panel furthermore comprises a liquid crystal layer sandwiched between two transparent substrates. The back light module provides a surface light source to illuminate the liquid crystal panel for displaying images.
FIG. 1 is a cross-sectional view of a conventional straight down back light module. As shown in FIG. 1, the back light module 100 comprises a frame 102, a reflecting plate 104, at least a lamp 106, a diffusion plate 108, an optical film 110 and at least a supporting column 112. The reflecting plate 104 is set on the bottom interior surface of the frame 102. The lamp 106 is set within the frame 102. The diffusion plate 108 is positioned over the frame 102. The optical film 110 is set over the diffusion plate 108. The supporting column 112 is positioned within the frame 102 between the diffusion plate 108 and the lamp 106. Through the supporting column 112, the diffusion plate 108 is prevented from twisting deformation that might lead to a change in the optical characteristics of the back light module 100.
FIG. 2 is a cross-sectional view of another conventional straight down back light module. As shown in FIG. 2, the back light module 200 comprises a frame 202, a reflecting plate 204, at least a lamp 206, a diffusion plate 208, an optical film 210 and at least a base stand 212. The reflecting plate 204 is set on the bottom interior surface of the frame 202. The lamp 206 is set within the frame 202. The diffusion plate 208 is positioned over the frame 202. The optical film 210 is set over the diffusion plate 208. The base stand 212 is attached to the frame 202 underneath the lamp 206. Using the base stand 212 to support the lamp 206, possible deformation of the lamp 206 that might lead to a change in the optical characteristics of the back light module 200 is prevented.
Although the supporting column 112 inside the back light module 100 in FIG. 1 is able to support the diffusion plate 108 and prevent distortion, the lamp 106 cannot be supported by any elements. When the size of the liquid crystal panel is increased, the dimension of the lamp 106 will also correspondingly increase so that the lamp 106 may sag due to insufficient stiffness. Thus, there will be some possible changes in the optical performance of the back light module 100.
On the other hand, although the base stand 212 within the back light module 200 in FIG. 2 is able to support the lamp 206 against sagging deformation, there is no specific structural support for the diffusion plate 208. When the size of the liquid crystal display panel is increased, dimension of the diffusion plate 208 will also correspondingly increase so that the diffusion plate 208 may warp due to insufficient stiffness or thermal expansion. Hence, there will be some possible changes in the optical performance of the back light module 200.